Bilingual language switching and the frontal lobes: Modularity control in language selection

Bilinguals typically show a cost of switching between their two languages. When asked to name single numerals rapidly and unpredictably in one or the other language, nonbalanced bilinguals demonstrate markedly slower responses on switch trials. This language switching cost is consistently larger when switching to the speaker's stronger, dominant language (L1), resulting in a crossover such that L1 responses are slower. To ascertain the brain mechanisms mediating the control of language switching, switching was examined in a bilingual patient with frontal lobe damage and impaired control processes, FK. While FK showed RT language switching costs well within the normal range on successful switch trials into the dominant language, he made an inordinately high number of erroneous dominant language responses when required to switch from the dominant language to the nondominant language. In addition, FK showed comparatively greater difficulty in maintaining the nondominant language across trials. FK's deficits are attributed to problems in modulating inhibitory resources across trials in a dominant language system